The present invention relates to locking mechanisms for holding a head arm assembly in place when power is off.
Disk drives have a head arm for positioning a head above a disk to read data from the disk and write on to the disk. This head arm is moved with either a rotary or linear actuator. When power is removed, the head arm is moved so that the heads are placed at the edge of the disk or near the center of the disk away from the data in the middle portion of a disk. This is done to prevent the heads from contacting the disk near the data portions and damaging the data. Typically, upon loss of power, a capacitor is discharged or a motor winding is switched to provide the necessary power to move the head arm assembly to its parking position. A limit stop is provided to stop the movement of the head arm assembly, incorporating a shock absorption mechanism to absorb the shock of a fast moving head arm as it engages the limit stops. A solenoid actuated brake or locking mechanism is typically used to hold the head arm in place after it contacts the stop.
However, if the brake or locking mechanism is not engaged, the head arm can move outward and damage the recording surfaces of the heads or the disk. One mechanism which is used in place of a brake or mechanical locking mechanism is a magnet. Such a magnet is shown in U.S. Pat. No. 4,594,627. The magnet is used to hold the head arm assembly in place when it contacts the mechanical stop. As shown in the '627 patent, the magnet is mounted on the bobbin of a linear motor for a linear head arm actuator.
As discussed in U.S. Pat. No. 4,562,500, the purpose of such a magnet prevents the head arm from operating too close to the magnet, for the motion of the head arm can be influenced by the locking magnetic field. This constraint places a limit on the number of data tracks which can be placed on a disk, since data tracks near the stop position can not be accurately read without supplying more power, due to the effect of the magnet stop on the head arm during a read/write operation.
The disadvantages of a magnetic latch are overcome in the '500 patent through the use of a mechanical locking mechanism.
An alternate method to the mechanical latching mechanism is the use of a weaker magnet whose field will not extend as far, and thus will not interfere with the read/write operation. However, the head arm assembly may become separated from the magnet when the disk drive housing receives a large shock.